There is no dependable general way of quantifying the times at which an average virus reproduces. In macroscopic terms, what are the litter sizes and breeding times of an "average" virus in a culture? This project develops mathematical and experimental techniques for determining the average number of daughter virions from a single mother virion, when these daughters attach to their cell, the average cycle time for the daughters, and the standard deviation (spread) of the viral cycle time. These determinations can be made from flow cytometry experiments. Target cells are stained with lipid dyes, and viruses syncronized at their attachment phase by incubating them with the stained "generation 0" cells. By collecting data on a marker of infection (in actual experiments, this will be gp41 in HIV), both in generation 0 stained cells and unstained cells that are added later and incubated with the infected "generation 0" cells, the reproduction of the average virus can be determined as the solution of an integral equation. The same methods can in principle be employed in calculating litter sizes and breeding cycle times of an animal, after a homogeneous group of the animals is released into the wild and several populaton counts taken. In the medical context, however, this work is intended to improve the quantitation of various HIV therapies and their inhibitory effects on HIV reproduction. Computer programs are now in place, a theoretical paper has been published, preliminary experimental data have been analyzed. We are currently improving the experimental protocols with new cell staining methods.